When will Black Australorp females get their combs?

[Sparklewina]

I'm not exactly sure where to put this post so I hope this is an okay place. I have two black australorp pullets hatched 1/31/2012. They are nearly fully grown (at least compared to my Rhode Island Red adult hen) but they have almost no combs at all. Literally there is just a teensy little mohawk on each of their heads a few milimeters high at the most. When I look at pictures of australorps they all have combs and wattles and my girls have none. Do these grow in at an older age?

 

[themenagerie]

I have a Black Orpington pullet (they're very similar to Australorps) who was born last summer..somewhere around the end of July and she didn't grow a comb until this spring, she just had a flat grayish comb, then all of a sudden almost overnight it grew and turned red